Resilient takeup means for use with screw threaded fasteners



July 5, 1960 A. v. c. DAVIS RESILIENT TAKEUP MEANS FOR USE WITH SCREW THREADED FASTENERS Filed Jan. 15, 1954 :wm i

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nited States atent 2,943,870 Patented July 5, 1960 RESILIENT TAKEUP MEANS FOR USE WITH SCREW THREADED FASTENERS Allen v. c. Davis, Burbank, Calif. (5600 Alta Canyada Road, La Canada, Calif.)

Filed Jan. 15, 1954, Ser. No. 404,303

1 Claim. c1. ass-200 This invention relates to spring takeup means for use with fasteners and more particularly to a resilient takeup means for use with bolts and screws characterized by capacity to exert an unusually high value of takeup force over a substantial range of movement and at the same time being of very small size.

An example of a use in which such action and capacity is required is in the inlet and outlet connections for fuel cells in aircraft. These fuel cells are generally formed of rubber or equivalent flexible and resilient material with an inner lining of a thin membrane of nylon or other material which is more resistant to the effects of the fuel than the material constituting the walls of the fuel cell. The inlet and outlet connections to the fuel cells generally comprise flanged fittings secured to the outer face of the cell wall in alignment with an opening therethrough by a series of screws extending through openings in the fitting flange and through the cell wall and threadedly engaging threaded holes in a washer on the inner face of the cell wall; the said threaded holes extending only from the face of the washer engaging the cell wall to prevent the possibility of fuel leakage along the threads of the screws. The cell wall material while initially resilient, tends to lose apart of such resilience through aging as well as through the effects of extremes of temperature deriving from altitude and heretofore unless frequent checks were made to be sure that all flange screws are suificiently tight as measured by application of a torque indicating wrench, there was constant danger of fuel leaks developing with usually complete destruction of the plane and probable loss of life.

Within the allowable space limitations together with the extent of takeup action desired without such loss of exerted force as to allow leaks to exist no simple helical spring could be calculated to meet the specific requirements. The desired type of action was that of a volute spring in which the successive coils bottom on the base on which the large end of the spring rests, but space limitations prevented the use of such a spring.

With the foregoing considerations in mind, the principal object of the invention is the provision of a resilient takeup means for use with screw threaded fasteners such as screws and bolts characterized both by small size and by spring characteristics which resemble those of a volute spring.

Another object of the invention is to provide a spring takeup means for use with bolts and screws which in uncompressed condition resembles a simple helical spring, but which in use utilizes the end efiect of the spring to achieve the high resistance to final compression and accordingly reacts in the same high degree in its action as a takeup.

With the foregoing objects in view, together with such additional objects and advantages as may subsequently appear, the invention resides in the provision of a spring takeup means for use with screws described by way of example in the following specification of one mode of execution of the invention; reference being had to the accompanying drawings which form a part of said specification and in which drawings:

Fig. 1 is a top plan view of a portion of a fuel cell showing the attachment of an orifice fitting thereto,

Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1 showing the invention applied thereto,

Fig. 3 is an enlarged end elevation of a spring takeup means such as shown in Fig. 2,

Figs. 4 and 5 are respectively, diametrically opposite side elevational views of the spring takeup means shown in Fig. 3,

Fig. 6 is a flat development of the unstressed spring takeup means shown in Fig. 3 as though opened on the line 66; the figure being modified by the showing of the cross sections of the ends of the portions of the takeup at the line 66,

Fig. 7 is a view similar to Fig. 6 but showing the relative positions of. the portion of the takeup means at the time of the initial contact of the portions incident to compression by a bolt or screw passing therethrough, and

Fig. 8 is a view similar to Figs. 6 and 7 but showing the action of the takeup means incident to final tightening with incident energization of those portions constituting the end effect of the takeup means.

Referring to the drawings, the illustrated embodiment of the invention comprises a helical spring 1 of approximately two complete coils; the ends of the coils being ground square with the axis of the spring and the thus flattened end portions extending through at least slightly more than and preferably considerably more than half of the circular extent of the end faces as shown in Fig.

3. In the illustrated embodiment, the spring is formed of round wire; a portion of the outer diameter of the wound spring thereafter being removed by grinding to meet specific space requirements, but for, all practical purposes having to do with the action of the spring as a takeup means in the manner with which the invention is concerned, the said reduction of the outer diameter or other cross sectional form of the wire from which the spring is formed is of no significance. As formed for installation, the spring is givena helix angle that will produce a space between the adjacent sides of the convolutions which is substantially equal to half the distance through which the uniform takeup action isdesired.

Referring to Figs. 1 and 2, the invention is shown applied to screws S securing afitting F to the resilient, compressible wall of a fuel cell C; the screws-passing through aligned holes in the fitting and cell wall and engaging threaded holes H in'a washer W on the inner wall of the fuel cell wall. Each of said screws is provided with a takeup means embodying the invention; the screw at the left hand side of Fig. 2 being shown in the position occupied at the beginning of the tightening action and at the time at which the resistance to compression of the resilient cell wall is approximately equal to the resistance of the spring to initial compression, while the right hand screw is shown in completely tightened condition.

Referring next to Fig. 6 the spring is shown opened out into a straight line as indicated by the broken lines in Fig. 3; the figure being modified by the showing of the cross sections of the portions theoretically cut in thus opening the spring and the spring being in uncoma pressed condition as at the left hand side of Fig. 2. Due to the fact that the squared ends of the spring are each of greater than a half revolution in extent, as the screw S is tightened; the torsion in the body of the spring first causes the coils to be moved toward each other in the axial line of the spring until they touch at the point in the spring most remote from both ends of the wire, i.e.,

a-point diametrically opposite the ends of the wire. In

"the illustrated embodiment of the invention, the screws are A dia. having 28 threads per inch and the retorque to bring-the coiis'r iintoithisinitial-gcentact ;as:-shdwn in Kg, 7 zand"with:the attendantislight tcornpression of the cell wallris about 20-iinchepounds. :The iontinued tightening" of filE SCIfiW-{CZIUSCS 'both;ends of the 'spiing stozigradually bottom won -theadiaceirt convolution'lprogressively irom -the point-1of;initial contact to the final co'rnplete closure :of-;the spring. *This action resembleshthe :bottom'ingfidf the coils ofga volute spring but difiers in that identicalgactionis place at both Y ndswf the-:spting tncl in that the .cross,sections-: of the V V deflected ends is sprogressivelyedecreasing ;as :;the -;de-

flected portionsgrow shorter in length The actualresult is th'at t-he 'torque values trisealmo'st vertically until at about 80inch pounds thel entireclengthiofathe spring is ol'osed spring are of: course: nor-longer in parallel: relation,

but in the illustrated use of the inventiom-Lt'ne screwis distorted so' that the underside 'of' the head is parallel with the outer end of the aspr-ingr andthere may ,also' be some accornniodating deflection or I boththe washer and the fitting-flange. WhileV'the illustratedfspring'has a total range of compressibility of about, say 0.075", inythe aJctuah il1ustrated use,the fuelcells aredisca'rded when y i'eason' of: aging-the engagedz portion 1 of: :the cell wall -hes'aecreasea to a normal thicknessbt about; say, 0.03 a to 0,040 less than its original thickness -andlat such ii'rne th'ese springs will have :opened up to thepp'oint at which about 60 to 65-1neh pounds-oftorque wouldhave iiiitial ly brought them. Consequently,- the force exerted liy the; screws in' holding the fitting-tightly clamped to V V the f uel 'cell hasnot been 7 so adversely: afiected by such lirinlage ofhe cell Wall material'as to-allow leakage occur. While a spring 'oftwo complete turns appears most' desii'able some range in this respect is permissible b etvveem sayg-gl /i turns and'about 2% turns. Likewise;

a-the si-ze fof wire and angle of helix may-bevaried to s lt fll requirements of individual installations for other 40 uses. The inventionis' not intended-as a; rotation pre- ="-venting means but r'ath'er as a 1 means (to r provide a resiltween: 'scre'w or bolt connectedfparta Therefore, the'inventrontis not tobe' deerned to be limited to the-exact construction hereinabove disclosed b'y vvay of sp'ecfific examplq but to include as well -all such "modifications in I size it and shape: as \Vfill' as of the V 'c'rdss sectionof -the spring material asshall act in the hereinbefore described manner -for'sthe purpose of. providing 'sjir'in'g'tztkehpfor fastening devices.

enf takeup rneans of small overall:=size which is vcapable of 'exerting ran' nnusually high 'value of takenp -f orce -be-' laim: a r 7 In combination, a flexible and resilient fuel cellfor aircraft having an orifice in a wall of said fuel cell, a

metallic fitting attached to the outer faceof said wall 5 in alignment with said orifice, and means for securing said fitting'to said wall cornprising a flange on said fitting engaging the outer"faceof said wall, a washer of substantially; the; sameuinner and: u te 1' dianqteters aswsaid flange on 'the'iinnerifacefl s'ai wall andmaving a series of radially spaced threaded oles fprrned in thewall en-- bolts extending gaging e fi m y. s ebfia "s r e 6 through said flange and sa'id"willandthreadedlyengaging said threaded hol'es, ;and ;a pluralitymfi. resilient take- 7 up means mounted oneeach on each of said bolts between the headthereof"and the-outer surface of said h ng a i r diame Sl h lyda se tha -m s re -or- -boltr=with-whieh it is ttobe used; tsaid spring, when uncompressed havinglfiataend-faces {each ofrgreater'than V the gspring and then responding itoefurther compression by; progressive deflection-of the -ends of. thegspring into contact "with the adjacent convolution Lil-om said .first -increase of thetorquerequnedto deflect said ends after :said initialcontact being substantially greater than the rate of increase of=torque requiredto eflect said'initial Contact of ;the;convolutions of the spring.

" iReferencesfited inithefile,oflthis patent uNIr D"srA rEsmATENTs flange; each of said takeup means comprising a helical spring of substantially two complete revolutions and pointof contact until the decreasein length-oft the. un-- contacting portionof {the ends reaches -ZB 1'O;- tl1e rate .of 

